A Study on Fatigue Failure of Bicrystals by means of in site SEM-ECP Observation

众所周知，在软金属中，疲劳裂纹在持久滑移带(PSB)处形核。然而，PSB的特性与疲劳行为之间的关系还不是很清楚。本研究采用电子沟道方法(ECP)对铜单晶和双晶的拉伸变形和疲劳行为进行了研究。通过推拉疲劳试验研究了铜单晶在拉伸预应变下的疲劳行为：(1)预应变导致疲劳寿命增加；(2)预应变导致PSB断裂；(3)预应变显著降低了疲劳裂纹的形核和扩展速率。(4)预应变干扰了仅在疲劳试件中观察到的特征位错结构的形成。用选区电子沟道(SACP)方法研究了晶界对双晶变形行为的影响.(5)晶界附近的塑性变形行为可以用这种方法来评价.(6)晶界影响区(GBAZ)强烈依赖于晶界应变不相容.(7)晶界影响区随拉伸形变量的增加而增大.

It has been well known that in soft metals fatigue cracks nucleate at persistent slip band (PSB). However, the relation between the feature of PSB and fatigue behavior is not so clear. In this study, electron channeling pattern (ECP) method was applied to discuss about both tensile deformation and fatigue behavior of Cu single crystals and bicrystals.1. Fatigue behavior of Cu single crystals subjected to tensile pre-straining was studied by means of push-pull fatigue test.(1) It is found that pre-straining caused the increase of fatigue life.(2) Pre-straining caused the fragmentation of PSB.(3) Both nucleation and growth rate of fatigue cracks was prominently reduced by pre-straining.(4) The formation of characteristic dislocation structure observed only in fatigued specimens was disturbed by pre-straining.2. The effect of grain boundary on deformation behavior of bicrystals was studied by means of selected area electron channeling pattern (SACP) method.(5) Plastic deformation behavior near the grain boundary could be evaluated by this method.(6) Grain boundary affected zone (GBAZ) depended strongly on the strain incompatibility at the grain boundary.(7) GBAZ increased with the increase of tensile deformation.